Internally-clamped composite piezo-electric acoustic device



A. MCL. NICOLSON INTERNALLY CLAMPED COMPOSITE PIEZO ELECTRIC ACOUSTIC DEVICE April 8, 1930.

Filed Jan. 11, 1927 INVENTOR .58 ALEXANDER McLEAN NICOLSON BY 6 7 ATTORNEY 1p m I Patented Apr. 8, 193

UNITED STA TES PATENT OFFICE? ALEXANDER ucnnnn mconsou, on NEW YORK/J, n. Y. nssronon, BY mnsnnnssron- MENTS, T0 FEDERAL TELEGRAPH eoMPANY, A CORPORATION on cnnnomvm This invention relates to a piezo-elec'tric device, and more particularly, to an acoustic device, adapted for the conversion of fluctuating electromotive forces into sound waves,

and vice versa. It has been known for some time thatcrystals of certain substances, such as Rochelle salt, quartz, tourmaline, and the like, produce an electromotive force if subjected to physical stress or movement, andto be characteristic of my invention are set conversely, produce physical stresses or movement in response'tmthe impression of an electromotive force uponv them.

In my copending application, Serial No. 155,900, entitled Internally clamped com- 4 posite piezo-electric; torsion device,. filed Dec. 20, 1926, I have'shown. and described a modified form of composite piezo-electric crystal .particularly .adapted for torsional vibration, comprising a plurality of chemically and optically similar component piezoelectric crystals arranged so that piezo-electrictorsional vibrations of the individual component crystals may be integrated, and mechanically clamped into a single entity by means of, an elasticand preferably metallic tie rod passing internally through the composite device, and preferably through a plurality of component crystals.

I have discovered that such a composite piezo-electric device as I have described in the said application may be utilized in connection with an acoustic diaphragm to produce an acoustic device such as a loud speaker, ora microphone, and as a matter of fact, when properly constructed and arranged, will produce results never before Obtained.

It is an object of this invention to provide an acoustic device of high quality and high sensitivity.

It is still a further object of this inven-.

. tion to provide a piezo-electric acoustic device of high quality and high sensitivity at a relatively low cost. I 7

It is still a further object of this invention to provide a piezo-electric acoustic device of high quality and high sensitivity, characterized by extreme simplicity and reliability, at a relatively low cost;

5 It is still a further'object of this invention INTEBNALLY-CLAMPED COMPOSITE PIE-ZO-ELECTRIC ACOUSTIC DEVICE Application filed Janna- 11,1921 Serial No. 160,359.

to provide such a piezo-electric acoustic deforth with particularity in the appended claims. My invention itself, however, both as to its fundamental principles and as to its practical application, will best be understood by reference to the specification and accompanying drawing, in which Fig. 1 is a front elevation of a piezo-electric acoustic device according to my invention.

Fig. 2 is a side elevation thereof. Fig. 3 is a side elevation of a modified form thereof. 1 v

Fig. 4 is a front elevation of a still further modified form thereof. Fig. 5 is a front elevation of a still further modified form thereof. 1

Fig. 6 is a planview of a arrangement shown in Fig. 5.

In accordance with my invention, I select a multiplicity of piezo-electric crystals to be assembled into a composite device, in the manner shown and described'in my copenddetail of the ing application referred to above. The selec'- tion as therein stated, is preferably made 'by choosing crystals which are chemically and optically similar. For example. I may select a number of quartz crystals, being careful to separate the crystals of dextroasymmetry from those of laevo-asymmetry.

The composite piezo-electric device may be constructed of either ofthe components, but it is preferable to use in any one assembly, only crystals of the same asymmetry, as. otherwise the mechanical'vibrations of the one class will be mechanically 180 out of phase with those of the other class, which will interfere with the' proper functioning of the device, and may even cause its destruction.

In the case of other hemihedral crystals which occur only in right-handed or lefthanded forms, as the case may be, such for example, as Rochelle salt, it is not necessary to separate the forms. After the component crystals have been selected, I may then proceed to form an opening through each of the 5 component crystals,

and preferably symmetrically disposed within the crystal in any suitable way, as for example, by drilling or by cutting the crystal,

fluting it and cementing the parts togetherby placing the crystals one after another passing the same upon the elastic member by through the hole in the 7 crystal. After a suflicient number of component crystals have beeirmounted on the elastic member to pro vide the desired size of composite device, a suitable compression carrying member, such as a metallic plate, may be mounted upon the elastic member bearing against the uppermost crystal and the desired compressive force exerted upon the device by means of a suitable nut which may be formed to engage threads on the elastic member.

The component crystals, when arranged as described, will be lined up in a line parallel to the o-axis of the crystals. They may like- F wise be lined up in line normal thereto, as

'well, in which case, a su1table' compression carrying member resting upon the entire outermost row of crystals will be used so as 40 to distribute the stresses uniformly upon all of the crystals.

It may be found desirable in the case where considerable number of crystals are to be used, to provide a plurality of elastic membei s spaced at the various points with-respect to the composite crystal, whereby a more uniform distribution of the stresses may be effected. It may sirable to provide a plurality of composite devices on the same .base, and so arranged as to work each with the other.

Electrodes and leads thereto may beprovided, arranged as described in m appl1-' cation above referred to, and the c amping bolt may be used as an internal electrode, if desired. p

Also, for the purpose of mechanically reinforcing the crystals at the points of mechanical contact, metallic reinforcing plates may be arranged upon the crystals, which plates may be used as electrodes-if desired. As an alternative, the crystal, or salient portions thereof, may be reinforced by the application of melt thereto, said melt com- 65 prising Rochelle salt fused at a temperature parallel to the c-axis,'

also be found de-- controlled according to the amount of water it is desired to retain in the melt.

A suitable acoustic diaphragm, such for example as a relatively rigid cone Wlll be secured at some non-nodal point with respect to the mechanical vibration of the crystal device, and preferably in such manner that torsional vibration of the crystal causes axial or reciprocal vibration of the diaphragm. More than one diaphragm may be provided if desired; more especially, in the case where a plurality of crystal devices are mounted upon the same base plate, an acoustic diaphragm may be secured to each crystal device and so arranged as to vibrate in such manner as to give rise to compression or rarefaction waves starting in opposite directions simultaneously from the same sound source.

Referring now more particularly to Fig. 1, 1, 2, and 3, designate separate component piezo-electric crystals. A base plate 4 is provided having depression 4 on the entire side, adapted to permit the mounting of a nut thereon, as will hereinafter be explained. Each of the crystals is provided with an opening extending through the crystal parallel to the c-axis and preferably symmetri- Cally disposed withreference to the crystal. This opening may through the crystal with a drill of the proper size, or it may be formed by sawing through the crystal parallel to the c and b axes and cutting corresponding grooves in the thus exposed crystal surface after which the two parts of the crystal are cemented together: for example by means of Rochelle salt melt.

A corresponding opening is provided through the base plate 4 and a cap or stress distributing member 6 is provided, also having a-hole formed therein, and being of a suitable configuration to rest upon the outer surface of the crystal 3 and distribute the stress uniformly over the surface thereof. An elastic securing member or tie rod 5, preferably of metal, having ahead 6 formed on one end and having end, is provided, pass through the base plate.

A suitable acoustic diaphragm 60, which may be in the shape of a cone, of fibrous material such as paper, is.mounted upon cap or stress distributing member 6, provided with an extension 6 The diaphragm 60 may be secured to the extension 6 in any desired manner: for example, the arm 6 may be drilled to receive a link62, to which is secured a preferably metal carrier plate shaped to receive the center of the cone 60, which may be secured thereon, as. for example, by olting, gluing or shellacking.

The ap or stress distributing member 6 carrying the cone is placed upon the tie rod 5 after which the crystals 3, 2, a1 id 1, are placed thereon; finally the base plateisplaced of the proper diameter, to

be formed by drilling holes of the. crystals and suitable threads on the other generated by the vibration of the crystal de vice. As an example of a suitable electrode a construction, the tie rod 5. may constitute a common internal electrode, and individual girdle electrodes in the form of a belt of metal foil or auze may be applied to each crystal around the exterior thereof, all .of which girdle electrodes may be connected together. The piezo-electric acoustic device so constituted is ready for use and will function either as a means for converting electrical waves into sound, or as a means for converting sound Waves into electrical Waves by reason of the torsional vibration of the crystal device: that is to say, if an electromotive force be impressed upon the crystal device, one end of the same will. tend to rotate with respect to the other end and will thereby cause substantial reciprocation of the cone 60, or in the case of sound waves.

impinging upon the cone, these will cause reciprocation of the cone, which, in turn, will cause torsional stress in the crystal-device,

producing fluctuations of electromotive force corresponding thereto, and in either case the oscillatlons lmpressed upon. or derived from the crystal device may be amplified, as I by thermionic amplifiers, to the extent necessary or desirable.

Referring now to Fig. 2, I have shown the manner of reinforcing the component crystals against mechanical stress. I stance, 10, 1'1, 12 and '13 designate solidified coatings of cementor melt, the former comprising Rochelle salt from which about one fourth of the water has been removed,

and the latter comprising Rochelle salt heated "to a temperature controlled in accordance with the amount of water it is desired to retain in the salt, These coatings maybe brushed or otherwise applied'to the salient points or of the crystals to build up a reinforcing'fstiucture,,and allowed to hard en before the crystals are assembled. If necessary, the crystals may then be ground to remove excess material and leave smoothly fitting cooperating faces.

Also, metallic plates of the proper shape to rest upon a large crystal area may be used,

which may form end electrodes for the component crystals. I 1

Referrin now to Fig. 3, I have shown a piezo-electrle acoustic device assembled in a similar manner, from crystals 15, 16 and 17,

of different shape. In this instance, a filler In this inblock 18 may be provided under cap 6, for

the purpose of distributing the stress uniformly over the upper surface of crystal 17.

Referring now to Fig. 4, I have shown a modification in which a relatively large number of crystals are utilized,,arranged in lines parallel to the c-axisand also in lines nor-- mal thereto, and in which a plurality of tie rods are utilized. In this figure, 20 designates a suitable base plate, provided with a recess 20 in the under side.

The crystals 23,24, and 25, etc, are built up and arranged in the manner dictated by the size and shape and number of the various component crystals with the c-axes parallel,

so as to form a composite device of the size and shape desired. A cap member 30 of the proper size and shape to contactwith the top surface of the composite crystal structure is I provided, and member 30 as well as the crystal and base plate, are provided with suitable openings, permitting the passage of tie rods 31, 32 and 33 formed on their upper ends with heads 34, 35 and 36, and threaded on their.

lower ends to accommodate nuts 37 38 and 39, by means of which the cap may be drawn down upon the composite structure to place the desired compressive force upon the crystals.

.The cap 30 will'preferably be provided with an extension 30*, upon which may be secured a diaphragm 60 in a manner preyiously described.

Referring now to Figs. 5 and 6, I have shown a pair of composite crystal devices 50 and 51,which may be constructed in a manner similar to Figs. 1, 2 or 3, but mounted upon a single haseplate 52, and provided with arms 53v and 54 extending toward each other. The armsmay be in line with eachother, and their adjacent ends slightly spaced from each other, or they may e arranged parallel but laterally offset from each other with their adjacent ends slightly overlapping as' shown in Fig. 6, whereby a maximum motion of the two arms may be produced in response to the impression 'ofan electromotive force upon the device, or a maximum charge may be developed by the application of force tothe arms. I

A suitable diaphragm such as cone 65 may be secured to the arm 53 in a manner already described, and a similar cone 66 secured to the arm 54, with their apexes pointed toward each other.

' If the crystals are operated in parallel,

that is to say, electrodes provided so that the impressed electromotive force is applied to all of the crystals in the proper sense, each of the crystals will tendto vibrate inthe same direction thereby producing relative motion of. the diaphragms65 and 66, 180 out of phase,-whereby compression waves may be generated on each side of the device simultaneously and similarly for rarefaction waves.

- If it is desired to operate the two diaphragms and 66.mechanically in phase, the connection to one of the composite crystal devices may be reversed, which will accom-- plish the desired result.

While I have shown and described certain preferred embodiments of my invention, it is understood that modifications and changes may be made without departing from the spirit and scope of my invention, as will be understood by those skilled in the art.

Iclaim:

1. An acoustic device comprising, in combination, a composite piezo-electric device comprising a plurality of chemically and optically similar piezo-electric crystals, means for clamping said crystals in a single entity, said clamping means passing internally throughsaid plurality of crystals, said crystals being so arranged that piezo-electric torsional vibrations of saidindividual compo-' nents may be integrated, and an acoustic d1- aphragm secured to said composite device at a point ofmaximum piezo-electric response in a manner such that torsional Vibration of said device eifects vibrations of said diaphragm.

2. An acoustic device comprising in combination, a composite 'piezo-electric device comprising a plurality. of chemically and optically similar piezo-electric crystals of dif ferent slzes, metallic clamping means passing internally through said plurality of said crystals, said crystals being so arranged that piezo-electric torsional vibration of said individual componentsmay be integrated, and an acoustic diaphragm secured to said composite device at a non-nodal point-thereof in a manner such that torsional vibration of said device. 'efiects reciprocatory vibration of said diaphragm. 1

'3. An acoustic device comprising, in combination, a composite piezo-electric device comprising a plurality of chemically and optically similar component piezo-electric crys tals of heterogeneous size and shape, an elastic member passin internally through said" plurality of crysta ls said crystals bein 'so arranged that piezo-electric torsional vi rations of said component crystals may be integrated when electro-motive forcesare impressed upon said component crystals, a cap 56, secured to one of said crystals in amanner to be vibrated therewith, and an acoustic diaphragm secured to saidpap in such manner that vibration of said cap effects vibration Y of said diaphragm.

4. An acoustic device comprising, in combination, a composite piezo-electric device comprising a plura 'ty of chemically and optically similar component piezo-electric crystals of heterogeneous size and shape, a plu- 5. An acoustic device comprising, in combination, a base plate, a composite piezo-electric device comprising a plurality of chemically and optically similar component'piezoelectric crystals of heterogeneous size and shape, arranged with their c-axes parallel and with a plurality in rows parallel to the c-axes thereof, a

cap member disposed upon the uppermost layer of crystals, means for physically securing said base plate, said component crystals, and said cap together comprising a plurality of spaced tie rods passing internally through a plurality of said crystals, and an acoustic diaphragm secured to said device at a non-nodal point with respect to torsional vibration thereof, in such manner that torsional vibraof crystals disposed tion of said device efiec'ts vibration of said diaphragm.

6. An acoustic device comprising, in combination, a composite piezo-electric device comprising a plurality of chemically and optically similar component piezo-electric crystals arranged with their c-axes parallel and with a plurality of crystals in line parallel to the c-axes thereof, a cap, means for securing said component crystals and said cap in a .single entity, passing internally through said composite vice, and an acoustic diaphragm secured said device at a non-nodal point with respect to torsional vibration thereof, in such manner that torsional vibration of said deyice effects vibrations of said diaphragm for the reproduction of sound. 7 An acoustic device comprising, incombination, a composite piezo-electric device comprising a base plate, a plurality of composite piezo-electric devices mounted on said base plate, each of said devicescomprising a plurality of chemically and optically similar component piezo-electric crystals in stacked relation arranged with their c-axes parallel, said plurality of stacked crystals being dis-, posed in rows parallel to said axes, a cap, and means for securing said components and said cap in a single entity and to said base plate comprising an elastic tie rod passing internally through each cap, row of crystals and comprising an elastic tie rod In testimony whereof I hereunto aflix my I signature.

rality of spaced elastic members passing ini ALEXANDER M'cLEAN NICOLSON. 7 

